Nonadiabatic quantum pumping in mesoscopic nanostructures

TL;DR

This paper investigates nonadiabatic quantum pumping in mesoscopic nanostructures, revealing how periodic potentials induce valley structures in transmission that shift with frequency, affecting current asymmetry.

Contribution

It introduces a detailed analysis of nonadiabatic quantum pumping effects in narrow constrictions, highlighting the robustness and frequency dependence of valley structures in transmission.

Findings

Valley structures in transmission are robust at finite frequencies.

Energy shifts of valley structures depend on phase-velocity and electron direction.

Frequency dependence causes asymmetry in transmission and pumping current.

Abstract

We consider a nonadiabatic quantum pumping phenomena in a ballistic narrow constriction. The pumping is induced by a potential that has both spatial and temporal periodicity characterized by $K$ and $\Omega$. In the zero frequency ($\Omega=0$) limit, the transmission through narrow constriction exhibits valley structures due to the opening up of energy gaps in the pumping region -- a consequence of the $K$ periodicity. These valley structures remain robust in the regime of finite $\Omega$, while their energies of occurrence are shifted by about $\hbar\Omega/2$. The direction of these energy shifts depend on the directions of both the phase-velocity of the pumping potential and the transmitting electrons. This frequency dependent feature of the valley structures gives rise to both the asymmetry in the transmission coefficients and the pumping current. An experimental setup is suggested for a possible observation of our nonadiabatic quantum pumping findings.